The present invention relates to aluminum-zirconium antiperspirant salts with high peak 5 aluminum content. The present invention also embraces methods of making these antiperspirant salts and compositions containing these antiperspirant salts.
Aluminum-zirconium antiperspirant salts have been known for several decades. See, for example, U.S. Pat. No. 2,814,585 (Daley), U.S. Pat. No. 2,854,382 (Grad), GB 1,353,916 (Bolich), U.S. Pat. No. 4,331,609 (Orr), U.S. Pat. No. 4,775,528 (Callaghan), U.S. Pat. No. 4,871,525 (Giovanniello), U.S. Pat. No. 4,900,534 (Inward), U.S. Pat. No. 5,225,187 (Carmody), U.S. Pat. No. 5,296,623 (Katsoulis), U.S. Pat. No. 5,330,751 (Curtin), EP 653,203 (Rosenberg), U.S. Pat. No. 5,718,876 (Parekh) and U.S. Pat. No. 5,955,064 (Giovanniello). Some of these aluminum-zirconium antiperspirant salts are described as having enhanced efficacy, which means that they provide greater sweat reduction than conventional antiperspirant salts.
The enhanced efficacy salts are typically differentiated from conventional antiperspirant salts by reference to the various aluminum peaks that can be identified when the salt is analyzed by size exclusion chromatography, typically HPLC (high pressure liquid chromatography). A suitable chromatographic technique must be capable of resolving the Al into at least four distinct peaks (labeled peaks 2 (or 1+2), 3, 4 and 5), such as is shown in U.S. Pat. No. 5,330,751. Up to now, the enhanced efficacy salts have been described as having an increased peak 4 content or an increased peak 4 to peak 3 ratio compared to conventional salts. (In some cases, enhanced salts have been described as having increased “band III” content by some authors, depending on the chromatographic technique and nomenclature employed. Generally, bands I, II, III and IV of one system correspond to peaks 1+2 (band I), 3, 4 and 5 of the other system.) Typically, the known enhanced efficacy salts (measured as 10% solutions) have an HPLC peak 4 to peak 3 area ratio of 0.5 or higher, preferably at least 0.7, with at least 70%, preferably at least 80%, of the aluminum contained in peaks 3 and 4. Thus, the enhanced salts will typically have a peak 4 content of at least 30% of the total aluminum contained in all the peaks (measured by peak area). In contrast, conventional non-enhanced antiperspirant salts have a negligible peak 4 content or a peak 4 to 3 area ratio less than 0.2, typically about 0.1.
Up to now, no one has suggested that peak 5 content plays any role in promoting the efficacy of antiperspirant salts. Aluminum antiperspirant salts are available as 2/3, 3/4, and 5/6 aluminum chlorohydrate (“ACH”) depending on the Al:Cl ratio (Al:Cl≅1, 1.7 and 2, respectively). While 2/3 ACH has a higher peak 5 content (typically greater than 50%) than 5/6 ACH (typically under 10%), it is not known to have greater antiperspirant efficacy. (See, for example, Bretschneider et al, “Antiperspirant Efficacy”, in Proceedings of the 9th IFSCC Congress, Boston, Mass. 1976, pp. 263–75.) In fact, 5/6 ACH is the form used virtually exclusively in commercial antiperspirant products which contain ACH.
Of course, the most widely used antiperspirant products contain aluminum-zirconium salts because they are more efficacious, especially the enhanced forms, as described above, with high peak 4 to peak 3 ratio. Prior to the discovery of the enhanced Al—Zr salts, U.S. Pat. No. 4,331,609 suggested that Al—Zr salts with a metal to chloride ratio below about 1.3 (e.g., 1.25) may be more efficacious than salts with a higher metal to chloride ratio. However, this efficacy claim does not appear to have gained acceptance in the industry because salts with low metal to chloride ratios are not believed to have been produced in commercial quantities, at least not to any significant extent. More recently, U.S. Pat. No. 6,126,928 described certain polyhydric alcohol solutions of the salts described in the aforementioned '609 patent.
Generally, all of the commercially used aluminum-zirconium antiperspirant salts have a peak 5 content of less than 25%, more typically less than 10%. Recently, Westwood Chemical has introduced an aqueous aluminum-zirconium chlorohydrate solution (sold under the tradename WZR 35BX3), which is said to have stable viscosity (i.e. viscosity does not increase significantly during normal storage) and appears to be made in accordance with U.S. Pat. No. 5,955,064. This salt has a somewhat elevated peak 5 content in the 20–25% range and a relatively low peak 4 content, typically less than 15%.
The enhanced efficacy aluminum-zirconium antiperspirant salts which are currently available commercially have one significant drawback. They are unstable in aqueous solution, where they rapidly revert back to their non-enhanced state (for example, as evidenced by a significant drop in the HPLC peak 4 to peak 3 area ratio). Consequently, these enhanced antiperspirant salts are generally only available in powder form and must be formulated into finished formulations as suspended powders in order to retain their enhanced efficacy. One solution to this problem is disclosed in U.S. Pat. No. 6,042,816, where stable aqueous solutions are prepared containing a calcium salt in addition to the antiperspirant salt and an amino acid.
It would be highly desirable to provide enhanced efficacy aluminum-zirconium antiperspirant salts which are stable in aqueous solution. This would make it possible to use the enhanced salts in finished formulations that require an aqueous salt form, such as the currently attractive clear gel compositions which have been successfully introduced in recent years. It would also be highly desirable to provide an aluminum-zirconium antiperspirant salt which has even greater antiperspirant efficacy than those currently available.